This invention relates to high voltage vacuum interrupters of the type containing a shield within an evacuated glass envelope for preventing metallic vapors from condensing on the inner surface of the envelope.
The shield is mounted within the envelope by means of support ring mounted within the glass envelope. One arrangement for mounting the support ring consists of inserting the rim of the ring within annular recesses formed on the inner surface of the glass envelope. U.S. Pat. No. 3,048,682 discloses one method of providing annular recesses on the inner surface of the glass envelope.
U.S. Pat. No. 3,376,186 discloses a shield support ring assembly wherein the ring is embedded within the glass envelope by a centrifugal casting operation. U.S. Pat. No. 4,000,999 discloses a further method for forming a shield support ring within the glass envelope. U.S. Pat. No. 4,158,911 discloses a method for manufacturing a vacuum tight circuit interrupter which includes the step of vibrating the interrupter sub assembly to remove loose glass particles.
One of the problems inherent with embedding the shield support ring within the glass envelope is the occurrence of ionizable particles within the evacuated container. The particles reduce the dielectric strength of the electrode gap and cause the vacuum switch to become conductive below the design voltage. A major source of the ionizable particles has been traced to glass which has loosely adhered to the inner wall of openings in the shield support ring. Various methods for removing the glass prior to evacuation have heretofore proved ineffective.
The purpose of this invention is to eliminate the source of ionizable glass particles from shield support rings embedded within high voltage vacuum interrupter envelopes.